1. Field of the Invention
The invention relates to a cylinder block and an internal combustion engine where a spacer that defines a flow passage for coolant is provided in a water jacket.
2. Description of the Related Art
Generally, an internal combustion engine includes a cylinder block in which cylinder bores are formed. A water jacket, which surrounds the cylinder bores, is formed in the cylinder block. An introduction passage, which connects the inside and the outside of the water jacket, is formed in the cylinder block. Coolant is introduced into the water jacket through the introduction passage. The internal combustion engine is cooled through heat transfer from the wall surface of the water jacket to the coolant flowing in the water jacket.
In the water jacket, the heat transfers to the coolant at an upstream side, and then the coolant flows into a downstream side in a direction in which the coolant flows (hereinafter, referred to as “coolant flow direction”). Therefore, cooling efficiency is likely to be low in the downstream-side area in the coolant flow direction. Thus, the temperature of the upstream-side area is lower than the temperature of the downstream-side area in the coolant flow direction. That is, the temperature is likely to differ between the areas of the cylinder block. For example, the cylinder bores may be unnecessarily deformed by the temperature difference, and as a result, friction may be increased.
Accordingly, for example, Japanese Patent Application Publication No. 2006-90196 (JP-A-2006-90196) describes a technology in which a spacer is provided in the water jacket. In the technology described in the publication No. 2006-90196, the spacer divides the space inside the water jacket into a portion near the cylinder bores and a portion near the outer wall of the cylinder block. In addition, a plurality of ribs, which protrudes, is provided on the inner wall of the spacer to throttle the flow of coolant in the gap between the inner wall of the spacer and the outer walls of cylinder bores. The width of the ribs increases toward the upstream side. In the cylinder block, the effect of throttling the flow of coolant, which is produced by the ribs, increases toward the upstream-side area in the coolant flow direction. Accordingly, the flow speed of the coolant decreases, and the cooling effect of the coolant decreases toward the upstream-side area in the coolant flow direction. By employing the configuration to adjust the cooling efficiency in each area of the cylinder block, it is possible to reduce the temperature difference between the areas of the cylinder block.
In the cylinder block described in the publication No. 2006-90196, the flow speed of the coolant differs between areas of the water jacket. Thus, it is possible to reduce the temperature difference between the areas of the cylinder block.
In the above-described cylinder block, after heat transfers to the coolant in the upstream-side area of the water jacket in the coolant flow direction, the coolant flows into the downstream-side area of the water jacket in the coolant flow direction. Accordingly, the cooling efficiency in the downstream-side area depends on how the heat transfers to the coolant in the upstream-side area.
Thus, in the above-described cylinder block, there is a limit to reduction of the temperature difference between the upstream-side area and the downstream-side area. That is, improvement needs to be made to reduce the temperature difference.